1. Field of the Invention
The present invention relates to irradiation equipment used for applying synchrotron radiation. More particularly, the present invention relates to irradiation equipment that has a short beam duct length, is easy to handle and has a high efficiency in irradiating synchrotron radiation having a wide range of wavelength.
In recent years, increasing numbers of synchrotrons have been used in research and development. Electrons accelerated along a circular orbit in a ring-shaped synchrotron radiate so-called synchrotron radiation through irradiation equipment and into a work chamber.
2. Description of the Related Art
Synchrotron radiation has attracted considerable attention in many fields, such as the field of lithography technology and the field of semiconductor process technology. Because synchrotron radiation is irradiated from the synchrotron, which has a high vacuum, for example higher than 10.sup.-9 to 10.sup.-10 Torr, the irradiation equipment must have a high vacuum at an inlet side thereof. However, an exit side of the irradiation equipment is connected to the work chamber, which is normally at a low vacuum or atmospheric pressure.
In a first case of existing irradiation equipment, a beam duct is sealed with a beryllium (Be) window at the exit side of the irradiation equipment. The synchrotron radiation is irradiated through the Be window and into the work chamber. The pressure of the work chamber for this first case is determined depending on the synchrotron radiation being applied and can be, for example, from atmospheric pressure to a low vacuum of 10.sup.-1 to 10.sup.-2 Torr.
In a second case of existing irradiation equipment, the work chamber is directly connected to the end of the beam duct without the Be window. In this case, the pressure of the work chamber is determined based upon an overall exhaust capacity of the irradiation equipment. As a result, the work chamber is, for example, at a pressure of about 10.sup.-6 to 10.sup.-7 Torr.
In existing irradiation equipment, a plurality of vacuum systems are connected in cascade and form a differential exhaust system. These vacuum systems connect the irradiation equipment to the synchrotron, which has a high vacuum. Each vacuum system comprises a beam duct, an exhaust pump, a gate valve and an aperture plate.
FIG. 1 shows a schematic structure of existing irradiation equipment for applying synchrotron radiation. In FIG. 1, a synchrotron radiation beam 1 is injected into an inlet of a beam line 3 from a synchrotron 2. The synchrotron radiation beam 1 progresses along the beam line 3 and is output through a Be window 31 that seals the right end of the beam line 3. In this case, the work chamber and the subject to be irradiated are disposed outside the Be window and are, therefore, at atmospheric pressure.
The beam line 3 comprises a plurality of vacuum systems, each comprising an aperture plate 33 (33.sub.1 to 33.sub.n) having a center beam transmission hole 32, a gate valve 34 (34.sub.1 to 34.sub.n), an exhaust duct 35 (35.sub.1 to 35.sub.n) and pumps (not shown). The vacuum systems collectively form a differential exhaust system. The beam line 3 not only transmits the synchrotron radiation beam 1, but also suppresses gas molecules from flowing toward the high vacuum inlet side from the low vacuum outlet side. The Be window 31 that seals the end of the beam line 3 must have a high synchrotron radiation transmissivity and a high mechanical strength.
Existing irradiation equipment for applying synchrotron radiation has many drawbacks including the following problems. Because the aperture plates 33 that divide the beam line 3 into a plurality of sections and prevent the gas molecules from moving toward the high vacuum inlet side have beam transmission holes 32, overall exhaust efficiency is reduced. That is, the beam transmission holes 32 form a bypass for the differential exhaust system and reduce the overall exhaust efficiency. Even when the end portion of the beam line 3 sealed by the Be window 31 is evacuated to a pressure of about 10.sup.-6 to 10.sup.-7 Torr, the total length of the differential exhaust system is longer than 10 meters.
Also, when the synchrotron radiation beam having a wavelength range between a few angstroms to several tens of angstroms is required, which is a wavelength range widely used in a lithography process of semiconductors, attenuation of the beam by the Be window 31 can not be ignored. In order to reduce the attenuation, the thickness of Be window 31 is preferably reduced to be less than 50 microns. However, a Be window 31 having a thickness of less than 50 microns cannot withstand the pressure difference between the atmospheric pressure of the work chamber and the vacuum (10.sup.-6 to 10.sup.-7 Torr) at the beam exit end portion of the irradiation equipment.
When the wavelength of the synchrotron radiation beam is longer than several tens of angstroms, the attenuation in the Be window 31 increases still further. In this case, a Be window 31 cannot be used. As a result, the work chamber should be directly coupled to the beam line 3. This requires that the pressure in the work chamber be 10.sup.-6 to 10.sup.-7 Torr. Because of this vacuum in the work chamber, the subject for irradiation in the work chamber cannot be handled easily.